1. Field of the Invention
The present invention relates to a separation and extraction device for sheets which separates a sheet in a sheet stack and extract the sheet from the sheet stack, and in particular, to a separation and extraction device which vibrates and loosens a sheet stack to separate a sheet in a sheet stack and extract a sheet from the sheet stack.
2. Description of the Related Art
Coping machines, printers, automatic teller machines (ATMs) in banknote processing applications, mail processing apparatuses, and the like handle sheets (paper-like media) such as print sheets, bills, copy paper, postcards, envelopes, and certificates. These machines need to extract a sheet from a stack of plural sheets. The machines thus comprise a separation and extraction device for sheets (paper-like media). By way of example, a bill processing unit of an automatic teller machine repeats extracting a bill from a bundle of bills (stack of sheets) stacked in a money input and output unit or a storage safe box. The bill processing unit then inspects the extracted bill. Accordingly, the automatic teller machine comprises a separation and extraction device that always separates a bill from a bundle of bills.
For conventional separation and extraction devices that separate a sheet and extract the sheet (paper-like media) from a sheet stack, it is most important to precisely extract each sheet into the apparatus while preventing overlapping sheets from being introduced at a time. Stacked sheets (paper-like media) are in close contact with one another for a long time and thus often stick to one another. Thus, each sheet needs to be separated and extracted, reliably.
The separation and extraction devices are roughly classified into frictional type that apply a frictional force on a sheet stack to separate sheets from one another and vacuum suction type that apply both a vacuum suction force and a frictional force on a sheet stack to separate sheets from one another. The vacuum suction type extraction devices generally exhibit good extraction performance but disadvantageously require a large size and high costs and make much noise. The frictional type separation and extraction devices advantageously eliminate the need for a large size and high costs and avoid making much noise. However, an extraction mechanism such as a conveying roller or a belt depends on the frictional force of media and may cause an error during a separation and extraction operation.
To separate adhering sheets from one another, the conventional separation and extraction device exerts a strong extraction force on an extraction surface of a bundle of stacked sheets (paper-like media). The conventional separation and extraction device then peels off and brings out a predetermined number of sheets from the stack bundle. After the extraction, the extracted overlapping sheets are separated from one another by an overlap preventing mechanism or the like and conveyed into a sheet processing apparatus.
The overlap preventing mechanism is based on any of various schemes. A common scheme separates sheets from one another by passing overlapping sheets (paper-like media) through a narrow gap. For example, the following scheme is commonly adopted for ATMs, printers, and the like. A wide conveying and separating rollers rotating in opposite directions are arranged parallel to each other via a given gap. If overlapping sheets (paper-like media) are supplied to between these rollers, opposite forces are exerted on the sheets (paper-like media) to separate them from one another. With this scheme, a separating capability is improved by making the size of the given gap closer to the thickness of a single sheet (paper-like media). However, normally, the mere adjustment of the given gap is often insufficient. A bundle of firmly adhering sheets (paper-like media) may block and lock the gap as it is, thus shutting down the apparatus. Such modification occurs frequently.
More specifically, in ordinary frictional separation and extraction devices, stacked sheets are supplied from the bottom of the device along a sheet feeding board. The top surface of the stack is in contact with a feed roller of a feed mechanism. Rotation of the feed roller conveys the uppermost sheet of the stack to a device inlet port comprising an overlap preventing device. The overlap preventing device is composed of a pair of a forward rotating roller and a backward rotating roller arranged parallel to each other via a given gap. The gap is set at a value smaller than that of the thickness of two sheets. When overlapping sheets are passing through these rollers, the lower backward rotating roller returns all these sheets other than the uppermost one toward the bundle of sheets to prevent them from being brought into the apparatus. This prevents overlapping sheets from being brought into the apparatus as they are.
Ordinary vacuum suction type extraction devices use an extraction portion comprising a vacuum suction mechanism that sucks sheets. More specifically, the vacuum suction type extraction device uses a pump or compressor to draw the interior of a drum to a vacuum (negative pressure). The uppermost media of the stack is sucked into a hole formed in the periphery of the drum. The sheet is thus brought out. Specifically, stacked sheet media are fed from the bottom of the device along the sheet feeding board. The top surface of the stack is brought into contact with the vacuum suction feed roller, which then sucks and brings out the top sheet. The vacuum suction type extraction device utilizes the friction roller to exert a stronger extraction force than the frictional separation and extraction device. The vacuum suction type extraction device is thus suitable for fast processing apparatuses that can bring in sheets at high speed.
However, even with the vacuum suction type extraction device, the stacked paper-like media often stick to one another after a long, close contact. Even if a strong extraction force is exerted on the extraction surface in order to separate the paper-like media from one another, overlapping sheets are often brought into the apparatus. The vacuum suction type extraction device thus employs a method of, after a predetermined number of paper-like media are peeled off from the stack bundle, using an overlap preventing mechanism or the like to separate the overlapping sheets from one another and conveying one of the resulting sheets into the apparatus.
Like the frictional type separation and extraction device, the vacuum suction type extraction device adopts a scheme of passing overlapping paper-like media through a narrow gap. As is the case with the overlap preventing mechanism of the frictional type separation and extraction device, the separating capability is improved by making the size of the gap closer to the thickness of single paper-like media. However, the mere adjustment of the gap is often insufficient. A bundle of firmly adhering paper-like media may block and lock the gap as it is, thus shutting down the apparatus. Such modification occurs frequently.
Another overlap preventing mechanism is known which replaces the forward rotating roller and backward rotating roller arranged with the given gap between them. In this mechanism, a feature such as a spring is used to press the backward rotating roller against the surface of a sheet to exert a pressing force on it. This mechanism is effective in preventing the overlapping of sheets (paper-like media) from a bundle of sheets of different thicknesses.
As described above, this overlap preventing mechanism is readily locked if a bundle of firmly adhering sheets is brought into the overlap preventing mechanism. For example, when stacked and pressed, sheets such as picture postcards which have smooth surfaces and which are slightly adhesive adhere considerably firmly to one another. Consequently, when brought out from the feed roller, a bundle of such sheets is stuck between the forward rotating roller and the backward rotating roller. Even when sheared, these paper-like media are not separated from one another. This may lock the device.
Jpn. Pat. Appln. KOKAI Publication No. 2004-002044 is known as an improved technique. The background art in Jpn. Pat. Appln. KOKAI Publication No. 2004-002044 abuts a bar-like vibrating member located above media that is about to be brought out, against the front surface of the media across the width to vibrate the media. This reduces the adhesion among the sheets (paper-like media) to aid an overlap preventing mechanism. This scheme reduces the adhesion among the bundled sheets (paper-like media) before extracting one of the sheets (paper-like media). This avoids extraction overlapping paper-like media. In this overlap preventing mechanism, a bar-like high-frequency vibrating member with a length greater than the width of the sheets (paper-like media) is placed upstream of the feed roller to vibrate the paper-like media, while extracting one of them.
The friction reducing mechanism employed in the overlap preventing mechanism disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-002044 is not sufficiently effective when simply vibrating the paper-like media at a low frequency. The vibration frequency needs to be at least several kHz. The inventors' experiments show that in a vibration range from 5 to 10 kHz, the vibrating member makes a very loud noise, which affects the environment in which the device is used. Accordingly, the vibration frequency needs to be at least 10 kHz. However, a very high power of at least several hundred watts needs to be consumed to vibrate the entire vibrating member at a high frequency of at least 10 kHz, the vibrating member having a length greater than the width of the sheets. The power source required to drive such a large high-frequency vibrating member is very expensive. This is a major design problem.
The inventors' experiments also show that the appropriate adhesion between the vibrating member and the sheets is very important to vibration of the stack. A stack of, for example, envelopes or used bills does not always have a flat surface. However, the vibrating member disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-002044 is shaped like a plate. It is thus difficult to allow the vibrating member to adhere to the sheets all over the width. The vibrating member can pinpoint a contact position on the sheets but the vibration of the entire bar is only partly used. Consequently, vibration efficiency is very low. It is also possible to use more of the whole pressing force in order to allow the vibrating member to adhere to the sheets all over the width. However, this method presses the stack bundle hard from above, thus disadvantageously increasing the adhesion between the sheets. This produces the opposite effect.
As described above, the conventional separation and extraction devices do not produce the vibrating effect required to reduce the adhesion among the stacked media. Experiments also show that a smaller vibration area is more effective in vibrating the media at high frequency. It has also been found that the shapes and arrangements of the conventional vibrating members present problems.
For the background art disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-002044, it is important to prevent overlapping sheets from being brought out from the stack. The sheets are thus vibrated in order to improve the overlap prevention. However, the shape of the vibrating member is not optimum, resulting in reduced vibration efficiency. The power source required to drive the vibrating member is also large and expensive. As a result, this background art is not practicable.